[Devel] [PATCH rh7] vtty: Don't close unread master peer if slave is nonzero

[Cyrill Gorcunov]

When there are several files opened on /dev/console from inside
of a container and noone hooked on master peer, any close called
cause master peer to be freed with TTY_CLOSING bit set. So that
next "vzctl console $ctid $ttynum" call force kernel to allocate
new vtty pair and in result we can't login into the container.

We've woraround master close when there is an active slave assigned
but I miss the scenario when several fd = open(/dev/console) done and
then one calls for close(fd).

Lets test if master peer is about to close while there are still
active slave (and move it into vtty_release helper).

https://jira.sw.ru/browse/PSBM-41985
https://jira.sw.ru/browse/PSBM-41672

Signed-off-by: Cyrill Gorcunov <gorcunov at virtuozzo.com>
CC: Vladimir Davydov <vdavydov at virtuozzo.com>
CC: Konstantin Khorenko <khorenko at virtuozzo.com>
---
 drivers/tty/pty.c    |   27 +++++++++++++++++++++++++++
 drivers/tty/tty_io.c |    7 ++-----
 include/linux/ve.h   |    2 ++
 3 files changed, 31 insertions(+), 5 deletions(-)

Index: linux-pcs7.git/drivers/tty/pty.c
===================================================================
--- linux-pcs7.git.orig/drivers/tty/pty.c
+++ linux-pcs7.git/drivers/tty/pty.c
@@ -1259,6 +1259,33 @@ struct tty_driver *vtty_driver(dev_t dev
 	return NULL;
 }
 
+void vtty_release(struct tty_struct *tty, struct tty_struct *o_tty,
+		  int *tty_closing, int *o_tty_closing)
+{
+	lockdep_assert_held(&tty_mutex);
+	int pty_master;
+
+	if (tty->driver != vttym_driver &&
+	    tty->driver != vttys_driver)
+		return;
+
+	pty_master = (tty->driver == vttym_driver);
+
+	/*
+	 * Do not close master while slave is active.
+	 */
+	if (!*o_tty_closing && pty_master)
+		*tty_closing = 0;
+
+	/*
+	 * Do not close master if we've closing
+	 * not the last slave even if there is no
+	 * readers on the master.
+	 */
+	if (*o_tty_closing && !*tty_closing && !pty_master)
+		*o_tty_closing = 0;
+}
+
 static void ve_vtty_fini(void *data)
 {
 	struct ve_struct *ve = data;
Index: linux-pcs7.git/drivers/tty/tty_io.c
===================================================================
--- linux-pcs7.git.orig/drivers/tty/tty_io.c
+++ linux-pcs7.git/drivers/tty/tty_io.c
@@ -1756,11 +1756,8 @@ int tty_release(struct inode *inode, str
 			(o_tty->count <= (pty_master ? 1 : 0));
 		do_sleep = 0;
 
-#ifdef CONFIG_VE
-		if (!o_tty_closing &&
-		    test_bit(TTY_PINNED_BY_OTHER, &tty->flags))
-			tty_closing = 0;
-#endif
+		vtty_release(tty, o_tty, &tty_closing, &o_tty_closing);
+
 		if (tty_closing) {
 			if (waitqueue_active(&tty->read_wait)) {
 				wake_up_poll(&tty->read_wait, POLLIN);
Index: linux-pcs7.git/include/linux/ve.h
===================================================================
--- linux-pcs7.git.orig/include/linux/ve.h
+++ linux-pcs7.git/include/linux/ve.h
@@ -224,6 +224,8 @@ struct user_namespace *ve_init_user_ns(v
 extern struct tty_driver *vtty_driver(dev_t dev, int *index);
 extern struct tty_driver *vtty_console_driver(int *index);
 extern int vtty_open_master(envid_t veid, int idx);
+extern void vtty_release(struct tty_struct *tty, struct tty_struct *o_tty,
+			 int *tty_closing, int *o_tty_closing);
 #endif /* CONFIG_TTY */
 
 #else	/* CONFIG_VE */